Stabilized plastic polymer and process of producing the same



Or I Patented Man 1 l, 1941 STABILIZED PLASTIC POLYMER AND PROC- ESS 0F PRODUCING THE SAME Howard W. Starkweather, New Castle County, and

Arnold M. Collins, Wilmingto n, Deb, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No-Drawing. Application March 18, 1938, Seria In France March 18, 1937 This invention relates to the treatment of plastic polymers of halogen-2-butadienes-L3 and their homologues. More specifically it relates to the treatment of plastic polymers of chloro-2- butadiene-l,3 (hereinafter, for convenience, referred'to as chloroprene). More particularly, it relates to stabilization of the plastic polymers of these halogen dienes.

Many of the polymers of chloroprene and particularly those made in emulsion in the presence of certain modifying agents as disclosed, for example, in the copending applications of Starkweather, filed March 19, 1938,,and given Serial No. 69,739; Starkweather and Collins, filed March 19, 1936, and given Serial No. 69,737; and Starkweather and Collins, filed July 30, 1937, and given Serial No. 156,518; are soft and plastic when first isolated and lend themselves readily to the common operations of rubber technology such as milling, calendaring and tubing. On standing at ordinary temperatures or sometimes when allowed to warm during 'milllng, these polymers have a tendency to lose their plasticity and become tough and elastic, even in the presence of antioxidants, such as phenyl beta naphthylamine. Thus, on storage under ordinary conditions they show a decided tendency to lose their. plasticity within periods as short as three months and at temperatures of about 70 C. they exhibit this decided tendency within 24 hours. It thus becomes very dimcult or impossible 'to handle them with ordinary rubber machinery and hence their use is limited.

It is an object of this invention to maintain in the plastic conditionduring milling and storage heat curable plastic polymers of halogen-2- butadienes-1,3 and their homologues in which the hydrogen atom on carbon atom 3 is replaced by a hydrocarbon group, particularly, heat curable plastic polymers prepared by polymerizing the halogen butadiene or its homologue in the presence of modifying agents, preferably while themaintaining the plasticity of these polymers, 4

which means. however, does not substantially reduce their capacity to be converted under curing conditions to the strong elastic state-resemblingvulcanized rubber. Other objects will appear hereinafter. With these objects in mind-it has now been discovered that the plasticity of heat curable plastic polymers of halogen-2-butadienes-l,3 and their homologues of the general formula in which X is halogen and R is hydrogen or a hydrocarbon radical, particularly, polymers of this type prepared by polymerizing the halogen butadiene in the presence of modifying agents, preferably while it is emulsified in water, for exam-' ple, as disclosed in the copending'applications, identified above, may be retained within desired limits during storage for long periods of time and also under milling conditions without, however, substantially reducing their capacity to be converted under curing conditions to the strong elastic state resembling vulcanized rubber, by having present with them as stabilizers relatively small amounts of ammonium salts. The invention is particularly applicable to heat curable chloroprene'plastic polymers although it includes within its scope the stabilization of other halogen butadienes, such as bromo-2-butadiene-l,3. and chloro-2-methyl-3-butadiene-1,3. A more specific group of polymers which are much improved by stabilization are those obtainable by polymerizing the halogen dienes of the above general formula while they are dispersed in an acid aqueous medium in the presence of modifying agents. It will be apparent that of this latter group those obtained from chloroprene are preferred in view of the preference for chloroprene polymers already expressed and because of their many advantageous properties. Further information as to the polymerization of these halogen dienes in the presence of modifying agents may be had by referring to the aboveidentifled copending applications. a

The following examples are included in order to more fully illustrate the invention, and it should be understood that thesaexamples are given for this purpose alone. and that accordingly they are not to be construed as limiting the scope of the invention.

In these examples and throughout this application, whenever the term "plasticity number is used. it refers to the thickness in thousandths of an inch of a 2.5 cc. sample of the polymer in the form of a cylinder in diameter which has been. heated to 80 C. for minutes and then kept under a weight or five kilograms for three general, have a plasticity number less than 125.

iplasticity will vary inversely as the plasticity inumber, lower plasticity numbers indicating more plastic materials. It has been found that to be milled satisfactorily a polymer should, in

The term regs-in" is also used in this application and wherever it occurs herein refers to the 1 gain in thickness in thousandths of an inch of 101 the compressed sample, from the plasticity test,

when freed from pressure for one minute at 1 room temperature. For satisiactory milling this "regain should, in, general, be less than 25. In addition, it should be noted that whenever,

throughout these examples,-the term "parts is a used, it refers to parts by weigh A plastic polymer of chloroprene was prepared according to the method disclosed in a copend- 1 ing application of Starkweather and Collins, Se-

3 ing chloroprene in acid aqueous emulsion in rial No..156,518, filed July 30,1937, by polymerizthe presence of 0.75% of thioglycolic acid and l 0.06% of hydrogen sulilde (both based on the amount of chloroprene used). ished polymer containing no stabilizer or anti- The dried, iin- 1 oxidant was divided into two portions, .one of l which was treated with 1% of phenyl beta naphthylamine by incorporation on a rubber mill and was retained as a control.

The other portion was treated with 1% oi. phenyl-beta naphthyl- I amine and 2% of the compound to be used as. stabilizer on a rubber mill. The plasticity numbers and regain oi both samples were determined at once and after aging for 24 and 48 hours in anair oven at C.' The table below 5 gives the plasticity data thus obtained for poly- 1 mar treated and untreated with a. stabilizeras disclosed herein.

' Plasticity number and .Exin aiter aging at ample Agent added in addition to 7 C. ior- No. phenyl-b-naphthylamins Ohm. 241m. 48 hrs.

one (control) 77-2 127-4; 130-03 1 Octadecl trimothyl ammoum romide 76-2 80-1 104-2 None control)... 77-3 150-90 2 Dimet yl StenyP' amine hydl'obro de' 70-8 04-0 loo-o 3 None (control) 77-3 150-00 Steary amine hydrobromide.. 715-1 102-2 -3 4 one (control) 109-! 204-46 Oetyl yridlnium bromide..." 8H 111-0 132-86 None (control) 77-1 129-00 144-73 5 Tetramethyl ammo ium bro- 4 m 0.; 7H 102-2 11%1 6 None control) 77-3 150-90 o-Tol dine h drobromide. 82-2 118-2 126-72 7 one (control 109-7 Ammonium bromide. 79-1 101-4 137-103 8 %i iis'st'nmm i M n e onum iodgie' -3; 97-6 -32 -103 ""Stenyl" is a mixture of m and stearyl groups.

v It will be seen from inspection oi this table that all the ammonium salts added have a very pronounced effect in reducing the change 'in plasticityv on aging at 70 C. A similar improve- .6

ment over untreated polymer exists as regards the change oi plasticity at'room temperature. the test at 70 0. being used because it gives 1 in a few days data on change in plasticity which 1 require months to obtain at ordinary temperature.

. ammonium salts mentioned above; unsubstituted ammonium salts or those in which from one up to four or the hydrozen atoms of the ammonium group, NH4, are substituted by organic rad cal This invention is not limited to the use of the.

ass-mosmay be' used. These radicals maybe either unsubstituted hydrocarbon radicals (either aliphatic or aromatic)- or, for example, hydrocarbon. radicals in which one or more hydrogen atoms have been replacedby substituents such as Cl, Br, I, N02, and COCHa, as in 'stearyl dimethyl acetonyl ammonium chloride. The hy- 'drocarbon radical may be polyvalent and at-- tachedthrough two or more of its valences to the same nitrogen atom (as in the case of cetyl. pyridinium bromide used above) or to the nitrogen atoms of twoor more ammonium groups, as in the case of, the dihydrohalides of the diamines. The substituted ammonium salt is not necessarily a halide. For example, a salt such as phenyl trimethyl ammonium methyl sulfate, CsHs(CHa) aN-SO4-CH3 may be used eflective- 1y. For the purpose of the present invention, the term "ammonium salt is intended to include compounds of all the types mentioned above.

for use according tothe present invention further' illustrates the wide application of the invention: I 1 I Cetyl trimethyl ammonium bromide Phenyl dimethyl octadecyl ammonium bromide Cetyl'trimethyl ammonium methyl sulfate Tetra ethyl ammonium bromide Tetra methyl ammonium iodide Di-S tenyY' dimethyl ammonium chloride Di-StenyP dimethyl ammonium bromide Phenyl dimethyl iso butylammonium bromide Trimethylamine hydrobromide Dimethylamine hydrobromide Aniline hydrobromide Aniline hydrochloride o-Iloluidine hydrochloride p-xylidine hydrochloride Dicyclohexylamine hydrobromide Monoethylaniline hydrobromide Diphenyl guanidine hydrobromide Diortho tolyl guanidine hydrobromide Tetra butyl ammonium bromide Dibutyl distearyl ammonium chloride Benzyl butyl dimethyl ammonium iodide (133) (2) Xylidine hydrobromide Allylamine hydrobromide Di iso propylamine hydrobromide Tributylamine hydrobromide Diben'zylamine hydrobromide a-Naphthylamine hydrobromide N-dibutyl piperidinium chloride Isopropyl pyridinium bromide celerate the'change from a plastic to an elastic condition. The preferred compounds are the c,long chain hydrocarbon substituted ammonium salts and particularly the bromides containin having from 12 to 18 carbon atoms, for example, the longchain trimethyl ammonium bromides,

particularly. cetyl trimethyl ammonium bromide,

20 The iollowing list of ammonium salts suitable a straight chain aliphatic hydrocarbon group used with success inthe' polymers may vary from 75 about .1% to about 5%, or more based on the polymer. With lower concentrations, up to about 1% m the case 6: the sta ilizing agents of lower.

molecular weight, the effectiveness of the compound increases very materially with an increase in the amount of material present, but the increase rapidly falls off with higher concentrations, i. e., above about 2%. An excess of stabilizing agent appears to remain as inert material. Preferably, therefore, about 1 to 2%. based on the polymer, of the ,lower molecular weight stabilizing agents should be present. In the case of the stabilizing agents of higher molecular weight larger proportions may be required to produce similar effects.

For the purposes of this invention, these stabilizing agents may be added to the polymer at any time after the polymerization process has been carried to the point desired, in amounts such that the total amount of stabilizer present in the polymer after the addition is, at least, that amount which will produce a definite stabilizing effect, 1. e., about 0.1% to about 5% based on the weight of the polymer, as disclosed above. It is obvious that if the stabilizer is added to the dispersion and is one which is soluble in the dispersing medium, it is necessary to add a greater amount than the amount desired in the polymer because some will be carried 01! with the dispersing medium when the polymer is isolated. Also where the polymer is given any treatment following the addition or the adjustment of the amount of stabilizer desired, which results in a loss of an appreciable'amount of the stabilizer, it

should be replaced at a later stage of the process,

preferably during the final milling step, that is, if the amount lost decreases the amount present below the desired content.

It should be understood that mixtures of two or more of the stabilizing agents disclosed herein may be used and that, where two or more stabilizing agents are used, their effects are, in general, additive, i. e., if one is present and another is added, it will increase the stabilizing efiect. It is also possible to use a stabilizer of another class in combination with an ammonium salt of the type described herein. For example, an ammonium salt as described herein, may be used in combination with anaromatic mercaptan (the use of-whlch is broadly disclosed in a copending application of Walker, Serial No. 69,740, filed March 19, 1936.) It will be obvious, of course,

that two stabilizers which react chemically with,

each other so as to destroy their eifectiveness cannot be used together. The amount of stabilizer added should be, at least, such that the total amount of stabilizer present after the addition is sufficient to produce a definite stabilizing effect, 1. e., about 0.1% to about 5.0%, based on the weight of the polymer, as disclosed above.

The various ammonium salts which are included within the broad scope of this invention may be divided into classes. Thus, one class, which is a preferred class,would include those which are emulsifying agents. Another would include those which are not emulsifying agents but are water soluble or at least are much more soluble in waterthan'they are in the polymer. Still another would embrace those which are not emulsifying agents and are not appreciably soluble in water or, at least, are more soluble'in the present inthe polymer in small amounts as a re-' sult of their having been employed during the polymerization step. On the other hand, these salts as well as those which are substantially water soluble or at least are more soluble in water than they are in the polymer are preferably added after coagulation where emulsion polymerization is resorted to since if added to the dispersion, at most only a portion of the quantity added remains in the polymer after coagulation. If, however, the agent is not soluble in water, addition of it to thedispersion prior to coagulation maybe preferable particularly if the agent is substantially more soluble in the polymer than it is in water, for the reasons that addition to the dispersion facilitates thorough mixing of polymer and salt andpermits immediate stabilization of the polymer after it reaches the desired state of plasticity. Of course, if emulsion polymerization is not resorted to stabilization with any of these ammonium salts may be effected immediately after the polymer is obtained.

As disclosed above, however, even though the one or another procedure is preferred, the ammonium salt stabilizers may be added to the H rubber art. For incorporating the salt into the polymer dispersion, the former is dispersed,preferably in the same dispersion medium as used for the polymer by any of the known methods applicable to such a system. This process is often facilitated by first dissolving the salt in a suitable .solvent, such as benzene, which is not miscible with the water. Still other methods of incorporation will be obvious to those skilled in the art.

As disclosed above,the presentinvention is applicablegenerally to heat curable plastic polymers of halogen-2-butadienes-L3 and their homologues. It is particularly applicable, however, to polymers of these halogen dienes which are prepared by polymerizing the dienes in nomalkaline emulsion in the presence of a small amount of a modifying agent. The modifying agents herein referred to are those disclosed in the following copending applications: Starkweather, Serial No. 69,739, filed March 19, 1936, which discloses emulsion polymerization of chloroprene in the presence of sulfur dioxide as a modifying agent; Stark"- weather and Collins, Serial No. 69,737, filed March' 19, 1936, which has now. matured into U. S. Patent No. 2,163,250, granted June 20, 1939, which discloses emulsion polymerization of chloroprene in the presence of hydrogen sulfide as a modifying agent; and Starkweather and Collins, Serial No. 69,738, filed March 19, 1936, .and refiled July 30,

' 1937, as Serial No. 156,518 which discloses emulsion polymerization of chloroprene in the presence of organic modifying agents. The organic modifying agents which this latter case discloses are unpolymerizable acid-stable organic compounds which are capable of forming an addition prodnot with compounds of the general formula om=o-c==cm i i in which x is hydrogen and R is a member of the group consisting of'hydrog en and hydrocar boa-radicals under conditions of polymerization of such compounds of said general formula. This group of modifying agents includes the'following classes or organic chemical compounds:

(1) Unsaturated compounds containing one or more carbonyl groups adjacent to the double bond;-

. (2) Aromatic sulflnic acids;

(3) Aromaticmercaptans; (4) Mercapto-carboxylic acids; (5) Aliphatic mercaptans.

A preferred form of the invention is its application to heat curable plastic polymers of chloroprene prepared according to the processes described in these copending applications, particularly such as are prepared by polymerizing the chloroprene while it is dispersed in an acid aqueous medium. Polymers prepared in the presence of modifying agentsonay be quite plastic 7 and where rather plastic polymers are desired the particular applicability of the present process is obvious.

It will be noted that as disclosed in copending applications of Walker, Serial Nos. 69,740, and 154,212, filed respectively on March 19, 1936 and July 17, 1937, and many of the organic modifying agents disclosed in theStarkweather and Collinsapplication, Serial No. 156,518, filed July 30, 1937, are also effective as-stabilizing agents, and that many [of the ammonium salts, described herein as stabilizing agents, are useful as emulsifying agents in the modified polymerization processes which are described in copendlng applications, hereinbefore identified. Certain of these modity n agents are, however, largely consumeddurlng the polymerization under some conditions and the amounts of those emulsifying agents which are also stabilizing agents and which are present during the polymerization are frequently insumcient to produce the .stabilizing eflec't dejsired in the finished polymer or else a portion of them is lost during some stage of the process.

-In general, therefore, even. though there are present during the formation of a particular polymer some of the agents which are eflective, J both during the polymerization and as stabilizers, itmay be desirable to add additional stabilizing agent to the polymer after the polymerization has reached the desired stage or at some later stage of the process in order to obtain the desired stabilizing effect in the final product.

-In the aboveexamples, 1% ofan antioxidant,

such as phenyl beta naphthylamine-is added to the polymer along with the stabilizer. The antioxidant may be added at'any time after polymerizationhas reached the desired stage. Be-' sides serving as an antioxidant, materials such as phenyl beta naphthylamine also serve toarrest-polymerization in ,emulsion and may be added for that purpose'according to the processes disclosed 'in the above identified copending applications which disclose modified emulsion poly- -'merization. It is possible to employ an ammonium salt as a stabilizer without the addition of an antioxidant but since polymers in which both i thylamine to dants may are used are considerably more stable than those treated with an ammonium salt but no anti- I oxidant. the use ofsalt and antioxidant together is preferred. The amount of phenyl beta naphnaphthylamine.

- duced according to the employris about what is used in the above examplesri: e.. about 1%," based on the polymer. Equivalent amounts of other antioxibe used in place of the phenyl beta It is also possible to eflect the addition of the stabilizing agents disclosed herein by a contin- 'uous process as well see batch process. This is conveniently accomplished bybringing together a stream'of a dispersion of the polymer and a stream of a solution of the stabilizing-agent in such a manner that they are thoroughly mixed. The amount of stabilizer added is obviously readily controlledby controlling the rates of flow of the-two streams. Itis, of course, clear that the stream comprising the polymer need, 3 not be a dispersion and that comprising the stabilizer need not be a solution. Solutions of polymer or dispersions of the stabilizer may, for example, be used. Obviously, however, whether one or ,both streams be a solution or a dispersion,

means should be provided to mix them thoroughly, if thorough mixing does not otherwise take place.

Continuous emulsification combined with continuouspolymerization and also combined with continuous addition of antioxidant is disclosed in the copending applications, identified above,

which relate to modified polymerization and-the the polymer dispersion. This will serve to illustrate the method. Obviously continuous production of stabilized polymer may be obtained without rigidly adhering to the particular scheme described. The present invention, therefore, is

not limited to this exact method for continuous operation. I

It is also possible to incorporate the antioxidant, for example,-phenyl beta naphthylamine continuously in like manner, if anantioxidant is to be added. As disclosed above, the preferred procedure includes the addition of an antioxidant. The antioxidant may be added continuously, either as .a separate stream as disclosed in the applications describing modified polymerization or it'may be included in the same stream in which the stabilizer is included and, in fact,

this latter variation has been found to be very convenient.

The stabilizedpolymer dispersions of the present invention may be employed as such or the stabilized polymer 'made in a dispersion may be isolated as a plastic mass and used in the same ways that the polymers which are isolated as. plastic masses and then stabilized may be used.

The uses-of the polymer 'stabilized; according to this invention are the same as those enumerated in the copending applicationaabove referred to,

which disclose the modified polymerization, for the polymer dispersions and plastic masses proprocesses described in those applications. I c

The compositions produced 'by the process of this invention are novel as well as useful. These plastic polymer compositions possessthe novel property of remaining inthe plastic state for much longer periods than previously known com-' positions of such pomners, but are substantially Y as converted under curing conditions to polymers had not been treated with a stabilizer as described herein. The stabilized polymers ,exhibit no substantial tendency to lose their plasticity on storage under ordinary conditions for 1 periods substantially in excess of three months or in the accelerated aging test at 70 C. for periods in excess of 24 hours.

It is apparent that many widely difl'erent embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

We claim:

1. The process which comprises polymerizing chloro-2-butadiene-1,3, while dispersed in an acid aqueous medium, in the presence of 0.75% of thioglycolic acid and 0.06% of hydrogen sulfide, both based on the weight of'the chloro-Z-butadiene-1,3, then separating the polymer from the acid aqueous medium and incorporating with it about 1% of phenyl beta naphthylamine based on the weight of the polymer and about 2% of a mixture of cetyl and stearyl trimethyl ammonium bromide based on the weight of the polymer.

2. A composition comprising a heat-curable plastic polymer of a compound of the general formula C Hz=?-C=C H1 in which X is halogen and R is a member of the group consisting of hydrogen and hydrocarbon radicals having in chemical combination therewith an unpolymerizable acid-stable, organic modifying agent capable of forming addition products with compounds of the above general formula under conditions of polymerization of such compounds of the above general formula and also comprising a small amount of a hydrocarbon substituted ammonium salt.

3. A composition according to claim 2 wherein the compound of the general formula is chloro- 2-butadiene-L3.

4. A composition according to claim 2 wherein the compound of the general formula is chloro- 2-butadiene-1,3 and wherein the ammonium salt is a bromide having a long straight chain aliphatic group substituted for one of the hydrogens of the ammonium radical.

5. The process which comprises incorporating a small amount of a hydrocarbon substituted ammonium salt into a heat-curable plastic polymer of a compound of the general formula in which X is halogen and R is a member of the 75 group consisting of hydrogen and hydrocarbon radicals having'in chemical combination therewith a mercapto carboxylic acidand also comprising a small amount of a hydrocarbon substituted ammonium salt.

8. A composition according to claim 7 wherein the compound of the general formula is chloro- 2-butadiene-L3.

9. A composition according to claim '7 wherein the compound of the general formula is chloro-2- butadien'e-1,3 and wherein the ammonium salt is a bromide having a long straight chain aliphatic group substituted for one of the hydrogens of the ammonium radical.

10. The process which comprises incorporating a small amount of a hydrocarbon substituted ammonium salt into a heat-curable plastic polymer of a compound of the general formula capo-0:011! l in which X is halogen and R is a member of the group consisting of hydrogen and hydrocarbon radicals having in chemical combination therewith a mercapto carboxylic acid.

11. A process according to claim 10 wherein the compound of the general formula is chloro- 2-butadiene-1,3.

12. A composition comprising a heat-curable plastic polymer of a compound of the general formula capo-0:011,

in which X is halogen and R is a member of the group consisting of hydrogen and hydrocarbon radicals having in chemical combination therewith an aromatic mercaptan and also comprising a small amount of a hydrocarbon substituted ammonium salt.

13. A composition according toclaim 12 wherein the compound of the general formula is chloro- 2-butadiene-1,3.

14. A composition according to claim 12 wherein the compound of the general formula. is chloro- 2'-butadiene-1,3 and wherein the ammonium salt is a bromide having a long straight chain aliphatic group substituted for one of the hydrogens of the ammonium radical.

15. The process which comprises incorporating a small amount of a hydrocarbon substituted ammonium salt into a heat-curable plastlc polymer of a compound of the general formula I on,=co=orn in which X is halogen and R is a member of the group consisting of hydrogen and hydrocarbon radicals having in chemical combination therewith an-aliphatic mercaptan and also comprising a small amount of a hydrocarbon substituted ammonium salt.

18. A composition according-to claim 1'! where- Y monium salt into a heat-curable plastic polymer 6 i v I a in the compound of the general formula is chloroclaim 117" z-butadiene-lfii 1 g 19. A composition according to wherein the compound of the general formula is ch1oro-2-butadiene-1,3 and wherein the ammoniumsalt is a bromide having at 1am; straightchaln aliphatic group substituted for one of the I hydrogens oi the ammonium radical.

20. The process which comprises incorporating a small amount oi a hydrocarbon substituted amot a compound of the general formula on,=o-c=om in which X is a halogen and R is a member of the butadien'c-L3. Y

of hydrogen sulfide and also comprising a small amount of a hydrocarbon substituted ammonium salt.

HOWARD w. s ranxwm'rrmn.

ARNOLD mcoums. 

